High voltage message waiting circuit

Abstract

A message waiting circuit comprised of a pair of electrical leads which carry a message waiting signal, a capacitor for storing electrical energy extracted from the message waiting signal, a transistor for allowing the capacitor to charge when the message waiting signal is within a predetermined range; a Darlington transistor for causing the capacitor to discharge; and a light emitting diode (LED) which emits light when the capacitor discharges. The flashing LED indicates that a message is waiting for a user of the telephone set associated with the message waiting circuit. Approximately ten to twenty-five message waiting circuits and associated telephone sets can be connected to a single telephone line.

We claim: 
     
       1. A message waiting circuit comprising: input means for receiving a message waiting signal from a PBX system, the message waiting signal indicating that a message is waiting for a user of a telephone set;   energy storage means for storing electrical energy extracted from the message waiting signal;   first circuit means for allowing the energy storage means to charge when the message waiting signal is within a first predetermined range and for isolating the energy storage means from the input means when the message waiting signal is within a second predetermined range;   second circuit means for allowing the energy storage means to discharge when the message waiting signal is within a third predetermined range; and   signaling means for emitting a signal when the energy storage means discharges, thereby indicating that the message is waiting for the user.   
     
     
       2. The message waiting circuit of claim 1 wherein the first circuit means comprises a transistor. 
     
     
       3. The message waiting circuit of claim 1 wherein the second circuit means comprises a Darlington transistor. 
     
     
       4. The message waiting circuit of claim 1 wherein the energy storage means comprises a capacitor. 
     
     
       5. The message waiting circuit of claim 1 wherein the input means comprises a pair of leads adapted for electrical connection to the PBX system. 
     
     
       6. The message waiting circuit of claim 1 wherein the signaling means comprises a light emitting diode. 
     
     
       7. The message waiting circuit of claim 1 wherein the third predetermined range is equal to the second predetermined range. 
     
     
       8. The message waiting circuit of claim 1 wherein the first predetermined range is between approximately minus sixty-eight volts and approximately minus one hundred and twenty volts and the second predetermined range is between approximately minus sixty-eight volts and approximately minus forty-eight volts. 
     
     
       9. The message waiting circuit of claim 1 wherein the second circuit means comprises at least one transistor. 
     
     
       10. The message waiting circuit of claim 1 further comprising a rectifier means for rectifying the message waiting signal before it reaches the first circuit means. 
     
     
       11. The message waiting circuit of claim 10 further comprising a first switch means electrically connected between the rectifier means and the second circuit means for allowing the first circuit means to be electrically bypassed when the first switch means is on. 
     
     
       12. The message waiting circuit of claim 10 further comprising a second switch means for allowing the message waiting signal to bypass the first circuit means and a terminal of the rectifier means when the second switch means is on. 
     
     
       13. The message waiting circuit of claim 1 further comprising a voltage sensing means for turning on the first circuit means when the message waiting signal is within the first predetermined range. 
     
     
       14. The message waiting circuit of claim 13 wherein the voltage sensing means comprises a Zener diode. 
     
     
       15. The message waiting circuit of claim 1 further comprising a charge control means for preventing the energy storage means from overcharging. 
     
     
       16. The message waiting circuit of claim 15 wherein the charge control means comprises a Zener diode. 
     
     
       17. A telephone system comprising: a plurality of individual telephone sets connected in series to a PBX system; and   a plurality of message waiting circuits, with at least one of the message waiting circuits being associated with each of the individual telephone sets and with each message waiting circuit comprising: receiving means for receiving a message waiting signal from the PBX system, the message waiting signal indicating that a message is waiting for a user of the individual telephone set;   energy storage means for storing electrical energy extracted from the message waiting signal;   first circuit means for allowing the energy storage means to charge when the message waiting signal is within a first predetermined range and for isolating the energy storage means from the receiving means when the message waiting signal is within a second predetermined range;   second circuit means for causing the energy storage means to discharge when the message waiting signal is within a third predetermined range; and   signaling means for emitting a signal when the energy storage means discharges, thereby indicating that the message is waiting for the user.     
     
     
       18. The message waiting circuit of claim 17 wherein the signaling means comprises a light emitting diode. 
     
     
       19. The message waiting circuit of claim 17 wherein the third predetermined range is equal to the second predetermined range. 
     
     
       20. The message waiting circuit of claim 17 wherein the plurality of individual telephone sets comprises five or more individual telephone sets. 
     
     
       21. A message waiting circuit comprising: a pair of leads adapted for electrical connection to a PBX and for receiving a message waiting signal from the PBX, the message waiting signal indicating that a message is waiting for a user of a first telephone set;   a capacitor for storing electrical energy extracted from the message waiting signal;   a first transistor for allowing the capacitor to charge when the message waiting signal is within a first predetermined range and for electrically isolating the capacitor from the pair of leads when the message waiting signal is within a second predetermined range;   a Darlington transistor for causing the capacitor to discharge; and   a light emitting diode which emits light when the capacitor discharges, thereby indicating that the message is waiting for the user.